[1] A shift power transmission apparatus is provided with an input shaft that receives engine drive force, a hydraulic continuously variable transmission that is driven by the input shaft, a planetary power transmission section that combines drive force from the input shaft and output from the hydraulic continuously variable transmission and outputs the combined drive force, and an output rotary member that outputs power to a travel apparatus.
Patent Document 1 describes a conventional example of a shift power transmission apparatus. The shift power transmission apparatus described in Patent Document 1 includes a pump shaft that passes through a hydraulic pump in a continuously variable shift section (hydraulic continuously variable transmission), and is configured such that drive force from the engine is inputted to the pump shaft on one side protruding from the continuously variable transmission, drive force from the pump shaft is transmitted from the other side of the pump shaft protruding from the continuously variable shift section to a compound planetary power transmission section, the continuously variable shift section is driven by the engine drive force, and the engine drive force and the output from the continuously variable shift section are combined by the compound planetary power transmission section.
[2] On the other hand, in a shift power transmission apparatus described in Patent Document 2, a power transmission system for transmitting output from the engine to front/rear wheels is provided with a hydraulic continuously variable shift apparatus (hydraulic continuously variable transmission), a planetary gear mechanism (planetary power transmission section), and two hydraulic clutches. When an HST (Hydraulic Static Transmission) mode drive train (HST mode power transmission) is configured by one of the two hydraulic clutches being connected, output from the engine is transmitted to front/back wheels after being subjected to speed change by the hydraulic continuously variable shift apparatus. When an HMT (Hydraulic Mechanical Transmission) mode drive train (HMT mode power transmission) is configured the other one of the two hydraulic clutches being connected, output from the hydraulic continuously variable shift apparatus is inputted to the planetary gear apparatus, the planetary gear apparatus combines output from the engine with output from the hydraulic continuously variable shift apparatus and outputs the combined drive force, and the combined drive force is transmitted to front/rear wheels.
Also, in the shift power transmission apparatus described in aforementioned Patent Document 1, a power transmission system that transmits output from the engine to a front wheel differential mechanism and a rear wheel differential mechanism is provided with a continuously variable shift section (hydraulic continuously variable transmission), a planetary power transmission section, and a forward/reverse switching apparatus. Output from the engine is inputted to the continuously variable shift section and the planetary power transmission section, and a planetary gear apparatus combines the output from the engine with output from the hydraulic continuously variable shift apparatus. The combined drive force outputted by the planetary gear apparatus is inputted to the forward/reverse switching apparatus and converted into forward drive force and reverse drive force, which is then transmitted to the front wheel differential mechanism and the rear wheel differential mechanism.
[3] There is a travel power transmission apparatus that includes a shift power transmission device. The shift power transmission device has a hydrostatic continuously variable shift section that operates so as to receive drive force from an engine and subject it to speed change, the speed-changed drive force to be output being subjected to speed change along an HST shift line, and a planetary power transmission section that operates so as to receive and combine the drive force from the engine and the speed-changed drive force from the continuously variable shift section, the combined drive force to be output being subjected to speed change along an HMT shift line by the speed change performed by the continuously variable shift section. The shift power transmission device is provided with a clutch mechanism that can be switched between an HST setting state, which is for setting HST power transmission in which the speed-changed drive force output from the continuously variable shift section is outputted to a travel apparatus, and an HMT setting state, which is for setting HMT power transmission in which the combined drive force output from the planetary power transmission section is outputted to the travel apparatus. The travel power transmission apparatus also includes a shift control module for, based on a shift instruction from a shift operation device, controlling shifting of a hydraulic pump included in the continuously variable shift section, and also controlling switching of the clutch mechanism.
In an agricultural apparatus for example, there are cases where there are repeated switches between forward and reverse, such as the case of changing direction at the end of a work line. The above-described travel power transmission apparatus has output characteristics such as those shown in FIG. 33, and is configured such that when operations for shifting forward and reverse via the neutral state of the continuously variable shift section are performed, the output speed changes to the forward side and the reverse side along the HST shift line, and thus it is possible to switch the apparatus between forward and reverse by merely performing a simple shift operation that does not require a special operation for forward/reverse switching.
In this type of travel power transmission apparatus described in aforementioned Patent Document 2, the power transmission system for transmitting output from the engine to the front/rear wheels is provided with a hydraulic continuously variable shift apparatus, a planetary gear mechanism, and two hydraulic clutches. An HST mode drive train is configured by performing connection switching with respect to the two hydraulic clutches, and in this mode, drive force output from a motor output shaft in the hydraulic continuously variable shift apparatus is transmitted to the front/rear wheels without being transmitted to the planetary gear mechanism. Also, an HMT mode drive train is configured by performing connection switching with respect to the two hydraulic clutches, and in this mode, drive force output from the motor output shaft in the hydraulic continuously variable shift apparatus is transmitted to the planetary gear mechanism, the planetary gear mechanism combines drive force from the hydraulic continuously variable shift apparatus with drive force from the engine, and the combined drive force output from the planetary gear mechanism is transmitted to the front/rear wheels.
[4] There is a travel power transmission apparatus that includes a shift power transmission device. The shift power transmission device has a hydrostatic continuously variable shift section that operates so as to receive drive force from an engine and subject it to speed change, the speed-changed drive force to be output being subjected to speed change along an HST shift line, and a planetary power transmission section that operates so as to receive and combine the drive force from the engine and the speed-changed drive force from the continuously variable shift section, the combined drive force to be output being subjected to speed change along an HMT shift line by the speed change performed by the continuously variable shift section. The shift power transmission device is provided with a clutch mechanism that can be switched between an HST setting state, which is for setting HST power transmission in which the speed-changed drive force output from the continuously variable shift section is outputted to a travel apparatus, and an HMT setting state, which is for setting HMT power transmission in which the combined drive force output from the planetary power transmission section is outputted to the travel apparatus. The travel power transmission apparatus also includes a shift control module for, based on a shift instruction from a shift operation device, controlling shifting of a hydraulic pump included in the continuously variable shift section, and also controlling switching of the clutch mechanism.
In an agricultural apparatus for example, there are cases where there are repeated switches between forward and reverse, such as the case of changing direction at the end of a work line. The above-described travel power transmission apparatus has output characteristics such as those shown in FIG. 50, and is configured such that when operations for shifting forward and reverse via the neutral state of the continuously variable shift section are performed, the output speed changes to the forward side and the reverse side along the HST shift line, and thus it is possible to switch the apparatus between forward and reverse by merely performing a simple shift operation that does not require a special operation for forward/reverse switching.
In this type of conventional travel power transmission apparatus described in aforementioned Patent Document 2, the power transmission system for transmitting output from the engine to the front/rear wheels is provided with a hydraulic continuously variable shift apparatus, a planetary gear mechanism, and two hydraulic clutches. An HST mode drive train is configured by performing connection switching with respect to the two hydraulic clutches, and in this mode, drive force output from a motor output shaft in the hydraulic continuously variable shift apparatus is transmitted to the front/rear wheels without being transmitted to the planetary gear mechanism. Also, an HMT mode drive train is configured by performing connection switching with respect to the two hydraulic clutches, and in this mode, drive force output from the motor output shaft in the hydraulic continuously variable shift apparatus is transmitted to the planetary gear mechanism, the planetary gear mechanism combines drive force from the hydraulic continuously variable shift apparatus with drive force from the engine, and the combined drive force output from the planetary gear mechanism is transmitted to the front/rear wheels.
Also, conventionally there is a apparatus that, as shown in Patent Document 3 for example, includes an actuator that controls the swash plate of a hydraulic motor included in a continuously variable shift apparatus, and is configured such that the actuator operates according to an instruction operation performed by a switching switch, thus switching the hydraulic motor between two stages, namely high-speed and low-speed.